Piezo-electric device



sniich R661 CROSS REFERENCE PIEZO-ELECTRIC DEVICE Filed May 6, 1927 G /P f 1 Patented Apr. 1931 UNITED-*STATES PATENT loli-wI-lclazj CHARLES B.'SAWYEB, 0F CLEVELAND HEIGHTS, OHIO, ASSIGNOR, BY MESNE ASSIGN- MENTS, TO THE CLEVELAND TRUST COMPANY, OE CLEVELAND, OHIO., A. CORPOBA- TION F OHIO Prezo-ELECTRIC DEVICE This invention relates to piezo-electric devices, and more particularly to an improved method of and means for utilizing the piezo effect of piezo-electric material;

Piezo-electric crystals such as, forv example, Rochelle salt crystals, have. been used in various devices, such as loud s eakers, transmitters and the like for trans orming sound pulsations into electric vibrations, and vice versa. `In general, an entire crystal has been employed and a twisting motion or longitudinal expansion of the crystal obtained when an electric field has been applied thereto. The crystals .so employed have been either of the clear type or of the composite type. The former type comprises a clear crystalline structure, whereas the latter type is characterized by porous or composite' portions at the ends fre uently known as hour-glass regions. With eit er type of crystal the mechanical deflection obtained is small unless'a relatively large crystal is employed, in which case the tone quality obtained is apt to suffer.

Thus with such large crystals the natural more, since suc `necessarily results in a non-uniform potential gradient and therefore non-uniform piezo-electric effect in various portions ofthe crystal, and in inefficient use of the piezo-electric m'aterial, since the thinner sections of the crystaly may be near the breakdown point due to the applied voltage when the thicker sections ofthe crystal are still capable of withstanding considerably higher voltages.

[fu-Moreover, when relatively small crystals are usci-mechanical levers are ,frequently necessarily employed therewith to mechanically magnify the movement of the crystal.

1927. sensi No. 189,141.

In s uch cases, `the natural period of the entire device, or of the lever itself, usually falls -within'the audible range,'resulting also in distortions" ordiscordant blasts or resonances.

Furthermore, when Rochelle salt crystals of the composite type have been employed lsuch crystals have been subject to changes in characteristics, due to loss of, or increase of, moisture content in the porous end regions.

An object of my invention is to provide a piezo-electric acoustic device of improved operating characteristics.

A further object of this invention is to provide a piezo-electric acoustic device of I greater eliciency. l

Another object of the invention is to provide piezo-electric acoustic devices .of uniform quality and characteristics.

A further object of this invention is the more eilicient utilization of a piezo-crystalline material of the Rochelle salt type.

Another object of this invention is to rovide a piezo-electric acoustic device in w 'eh the expansion of a piezo-crystalline material by an electric l'leld may be mechanically magnilied without the use of levers.

Another object of my invention is to provide Rochelle salt piezo-electric portions of uniform and improved quality and characteristics.

A further object of this invention is to p rovide piezo-electric crystalline portions of 1mproved character for use in acoustic devices.

Another object of the invention is to provide a slab of piezo-electric material of such characteristics that when suitably mounted and subjected to an electrostatic field, a point on said slab willhave a greater mechanical movementthan the expansion of said slab in any direction. Q.

y Other objects of the invention will be a parent to those skilled in the art from t e 'following description and annexedl drawings,

in which Figures 1, 2 and 3 are respectively'a top mg one manner in whiclila sla Yaccording to' -100 canse attestata "my invention may be obtained from this form of crystal;

Figs. 4, 5 and 6 are respectively a top plan view, end elevation, and front elevation of a slightly imperfect Rochelle salt crystal of the clear complete'type, the dotted lines in said figures illustrating one manner in which slabs accordingto this invention may be obtained from this form of crystal;

10 Figs. 7 and 8 are respectively a front elevation, and end elevation of a piezo-electric slab according to my invention, electrodes being vshown associated with the faces of said slab;

A Figs. 9 and 10 are respectively an end elevation, and front elevation of a piezo-electric device according to my invention, the device shown in Fig. 9 being arranged to -ae` tuate a cutting jewel, the device shown in Fig. 10 being arranged to actuate a loud speaker cone; I

F ig. 11 is a diagrammatic view of a piezoelectric slab illustrating the operation of said slab when mounted as shown in Figs. 9 and 10; and

Figs. 12 and 13 are respectively a to plan iview, and front elevation of a piezo-e ectric acoustic device similar to that shown in Fi 9, arranged for the cutting of phonograp 1 records.

In m present invention I cut or otherwise obtain rom a piezo-electric crystal or portion thereof, preferably though not necessarily of -Rochelle salt, a slab, which is preferably relatively thin, and whose faces are preferably arallel, and whose opposededges may also e parallel, as in the case of a rectangular or i square slab. While the slab is preferably rec-- tangular, it will be understood that other shapes may also be employed.

' In the case ofthe slab of square shape, the said slab is preferably so cut that the facs thereof are substantially parallel to the plane of major longitudinal and major transverse crystalline axes as hereinafter defined, a1- though certain of the advantages of my invention may be realized when said faces are not so disposed. Moreover, the slab .is preferably so cut that when an electrostatic field is-applied through the slab substantially perpendicular to the 'faces thereof, said sla will ltend to expand along one of its diagonals, or stating the proposition more generally, so that the slab will tend to expand in a direct1on at substantially 45 degrees to a major crystalline axis.

Y I may provide an improved acoustic device A according to the invention by suitably mounting a piezo-electric slab of the type above described. Thus, a square slab may be fixed to a suitable support at one edge, or a portion thereof. Suitable electrodes may then be dis- A posed on the faces ofthe slab whereby an electrostatic field may be applied through the -slab perpendicular to the faces thereof.

, y-55 When such electrostatic eld is applied, the

slab, if square, will tend to expand and contract along its diawonals, as will be more fully described hereina ter. By securingr a suitable acoustic member such as a loud speaker cone, phonograph record cutting jewel, or other member to the edge of the slab opposite to the fixed edge, said cone or other member may be caused to have a mechanical movement greater than the expansion of said slab in any direction, thereby effecting a mechanical magi nification of the slab expansion without the use of levers.

In Figs. 1, 2 and 3 is shown a Rochelle salt crystal 1 of the composite type having hourglass or porous end regions 2. The crystal 1 is shown as having the major lon itudinal estaca aan:

axis 0 0, the major transverse axis and I the minor axis a-a, said axes being mutually perpendicular. There is indicated in the ottedlines in Figs. 1, 2 and 3 one manner in which a slab according to my invention may be obtained from the crystal 1. The slab 3 is preferably so cut from the crystal 1 that itsI perfect Rochelle salt crystal of the clear complete type, the crystal 5 having the major longitudinal axis c-c, the major transverse axis b'-b and the minor axis a-a, said axes being mutually perpendicular. In the dotted lin-es at 6, 7 and 8 are indicated slabs which may be obtained or cut from the crystal 5. The faces of the slabs 6, 7 and 8 are preferably substantially parallel to the major crystalline axes c-0 and b-b. It will be understood, of course, that the dimensionsof the slabs cut from the crystal 5 and the number of slabs obtained therefrom will be dependent onl the number and size of slabs -desired and upon the size and quality of the crystal 5. y

In Figs. 7 and 8 are shown a piezo-electric slab 9 of my invention having associated therewith suitable electrodes 10 to which are connected suitable wires l1. The slab 9 is shown as being substantially square and as having the substantially parallel faces l2 and the opposed edges 13 and 14. The thickness of the slab 9 will depend upon the particular conditions to which the slab is to be subjected. Frequently, however, it is found advantageous to have the slab 9 relatively thin since in such case the mechanical movement of the slab due to the piezo-electrical effect may be obtained from relatively small applied voltages since it is well understood that the mechanical movement of the crystal In Figs. 4, 5 and 6 shown a slightly imlli l 'the crystal. While the slab 9 may perferab is 4dependent upon the volts per inch, or in other words, the potential gradient through be of uare or rectangular shape,it should be note that advantageous results may be obtained with slabs of various regular and irregular shapes, the shape of the `slab being dependent upon the particular use to which it is ut. l i

' ith the square slab 9 shown in Figs. 7 and 4 8 and cut or obtained from a crystal as hereinbefore disclosed, the expansion of the crystal upon application of an electrostatic field will take place along a diagonal AC or BD (Fig. 11 or, in other words, in a direction at substantially 45 degres's to a major crystalline axis. While certain advantages may be lobtained when the ex ansion of the crystal is at angles app'reciabljf4 greater or less than 45 de ees to said major crystalline axes, I have ound that in general the greatest effect is obtained when the crystal expands in the above described manner. The above-mentioned action of the slab 9 under an electrostatic field I have substantiated by numerous observations under a microscope.

In Figs. 9 and 10 I have shown a slab 9 suitably mounted to form an acoustic device of advantageous character whereb mechanical movement of an acoustic mem er greater than the mechanical movement or 'expansion of the slab 9 in an direction may be' obtained without the use o levers or equivalent means.

Thus the slab 9 is secured at a lower edge 13 to the base or support 15 by-suitable adhesive material 16 such as shellac, Canada balsam, The slab 9 may be secured to said support 15 along the entire edge 13 or portion thereof. AThelbase 'or support 15 is preferably of lead or similar heavy material which will remain stationary and not be affected by vibrations of relatively high frequency. To the faces 12 of the slab 9 are secured the electrodes 10 .such as of tin foil, said electrides covering preferably a relatively large portion of the said faces. Suitable wires 11 are secured to the electrodes l0 whereby the slab 9 may be subjected to a varying electrostatic field. To the u'pper edge 14 of the slab 9 is secured a clamp 17 by suitable adhesive material 18. In Fig. 9 a phonograph record cutting jewel 19 is shown associated with the clamp 17, the axis of the jewel 19 .being shown as perpendicular to the faces 12, whereas in.Fig. 10 is shown an acoustic diaphragm 20, such as a cone, securedto a socket member 21'in turn carried by a shaft 22. The shaft 22 which/is shown as parallel tothe faces 12 is carried by the 'clamp 17.

'the wires 11 to the devices shown in Figs.

V 9 and 10, the jewel 19 in Fig. 9 will vibrate the cone 20 will vibrate in a direction lon- 9 and 10 when subjected to a varying electrostatic field by means of the-electrodes 10.

The slab 9 in normal position when not subjected to an electrostatic field, is shown in the full lines ABCD, the lower edge AD` (13) being fixed in position as in the manner indicated in Figs. 9 and l0. When an electrostatic field is applied to the slab 9 in one direction throu h the electrodes 10, the slab 9, if the lower e ge were not fixed or restrained, would tend to elongate along the diagonal AC to the osition indicated by AE, the expan- -sion C being proportional to the strength of the electrostatic field. At the same time, if the lower edge AD were unrestrained, the

slab 9 would tend to contract along the n suming the position AB'CD shown in doti ted lines, the edges AB andv DC remaining parallel in the distorted position AB and DC. Upon ,the reversal of the direction ofd the electrostatic field, n the slab would tend to expand along the dia onal BD and contract along the diagonal Ag, the slab 9 assuming a position the reverse of that indicated in dotted lines in Fig. 11.

Assuming a point P on the upper edge BC (14) of the slab 9, at which point a clamp such as the clamp 17 in Figs. 9 and 10 may be secured, it will be noted that said point P moves to a point P when the slab 9 moves to the position ABCD.v The point P moreover would move to the point P if the electrostatic field 'were reversed. The distance traversed by the point P, namely PP and PP, when the slab is subjected to the aforementioned electrostatic field, are each greater than the expansion of the diagonal AC which is equivalent to the distance CE or the diiference in length between AC and AC. In effect, therefore, the point P, when the slab 9 is subjected to a varying electrostatic field, moves a greater distance than the expansion of the slab in any direction. It may be said, therefore, that a magnification is iven to the movement of an acoustic mem- 'er secured to the upper edge 14 of the slab 9 without the use of any levers or the like.

In Figs. 12.and 13 I have shown the application of a device such as shown in Fig. 9 to the cutting of phonographv master records Afrom a wax blank 23. Thus the turn table 24 may be .rotated about the spindle 25 and the wax blank 23 disposed over the uuper end of the spindle 25 on said turn table c5 a direction parallel to the faces 12, while 24. In operation, the slab support `15 may s I o be disposed in fixed position and the turn table 24 and record blank 23 rotated. The turn table moreover normally moves toward the cutting jewel 1 9 in order that a s iral groove may be cut in the blank 23. hen a varying electrostatic field is applied to the electrodes it will be understood from the previous description that the cutting ewel 19 will vibrate in such manner to cut a wavy spiral groove in the master blank 23, whereby to record the sound equivalents of the alternating wires 11.

It will thus be seen that I have provided a piezo-electric slab of advantageous characteristics, and that an acoustic member secured to said slab will be given a magnified 1l'rillpvement without the use of levers or the It will furthermore be noted that I have provided piezo-electric slabs of economical electromotive force applied to the l. characteristics in that a plurality of slabs may be obtained from a single piezo-electric crystal or portion thereof.

1urthermore, my improved piezo-electric slabs may be obtained from imperfect crystals or portions thereof ,thereby effecting great economy in the production of said slabs.

, It will also be noted that by means of my invention I may provide piezo-electric slabs and devices embodying the same of uniform dimensions and operative characteristics.

It will furthermore be seen that I have provided piezo-electric slabs of uniform and constant electric characteristics, since no vided a piezo-electric slab whose dimensions andthe descriptions herein trative and are not. intended to be in any porous Rochelle salt vcr stal end regions need be included in said slabs. Y

It will also be seen that I have provided piezo-electric slabs and devices embodying the same whose operating characteristics may be varied to suit thevoltages available, or to bring the impedance of said slabs closer to the desired tube impedance, as when said devices are used as loud speakers or record cutting devices.

It will moreover be noted that I have romay be varied to bring the natural period thereof to any desired value.

It will moreover be understood that my* invention is not limited to slabs formed Rochelle salts, but any suitable piezo-electric material may be utilized in the construction thereof.

To those skilledlin the art, many modifica-v tions of and widely dilfering'embodiments and applications of my invention will suggest themselves without departing from the spirit and scope thereof. My disclosures are purely illussense limiting.

What I claim is: 1. In an acoustic device of the class deexpand or contract in a direction substantially-` 45 degrees to the direction of movement of the acoustic member when said slab is acted on by an electrostatic field, whereby a motlon greater than the actual expansion or contraction of the slab in an direction is imparted to the acoustic mem er.

2. In an acoustic device of the class described, in combination, a support, asubstantially rectangular slab of piezo-electric material, said slab being so oriented with res ect to the crystalline axes that the slab tendli expand and contract in a direction substantially parallel to the diagonals of the slab, a portion of one edgeof said slab being secured to said support, an acoustic member attached to said slab adjacent an edge opposed to Said fixed edge whereby when said slab is subjected to an electrostatic eld said acoustic member is given a greater mechanical motion than the expansion or contraction of said slab in 'any direction.

3. In an acoustic device of the class described, in combination, a support, a slab of piezo-electric material, said slab being rigidly secured at one edge thereof to said support, an acoustic member secured to an ed e of said slab opposed to said fixed edge, sai slab being so oriented that when subjected to an electrostatic field said acoustic member will be actuated in a direction substantially parallel to the plane of one face of said slab and at right angles to a perpendicularfrom sai-d support through said slab, and vice versa.

In an acoustic device of the class de scribed, in combination, a support not ap reciably aifected b electrical or mechanlcal vibrations of au ible frequen a slab 'of piezo-electric material Vof the ochelle salt type secured at one edge thereof to said support, said slab having faces of substantially rectangular shape,'sa1d faces being substantially parallel to each other and to the "major crystalline axes, said fixed edge and opposed edge being substantially parallel to one ofL said major crystalline axes, an acoustic member secured to said opposed edge of said plate and arranged to function acousticall when moved in a direction parallel to the aces of said slab, electrodes secured to the faces of said slab'whereby when an electrostatic yfield "gaat Root is applied to said slab through said electrodes said acoustic member Awill have a greater movement than that of any elements of the slab in the direction of expansion or contraction.

5. In an acoustic device ofthe class de- I scribed, a support,a piezo-electric slab of the Rochelle salt type rigidly secured at one pogtlon thereof to said support, an acoustic mem- Rochelle salt type of substantially rectangular shape having faces substantially parallel to each other and to the major crystalline axes, means for supporting said slab at one portion thereof, and an acoustic member disposed at an opposed portion thereof, whereby the acoustic member will have a greater movement than the linear expansion or cont traction of any element of the slab.

7. In a piezoelectric device of the class de scribed, in combination, a support, a slabl of piezo-electric material of the Rochelle' salt type having faces substantially parallel to each other and to the major crystalline axis of the Rochelle salt crystal, said slab being secured along one of its edges to said support so that expansion and contraction of the slab upon the application of a electrostatic field takes place in a direction at an angle substantially less than 90 degrees to the supported edge, whereby a point on the opposite edge of the slab will have a movement greater than that of pansion or contraction. f 8. In a piezo-electric device of the class described, in combination, a support, a slab of piezo-electric material of the Rochelle salt type having faces substantially parallel to each other and to the major crystalline axis of the Rochelle salt crystal, said slab being of substantiall rectangular shape and having the longitu inal axis of the crystal substantially normal to two of its edges, said slab being supported on one of said edges whereby a motion greater than the expansion or contraction of the slab in any direction is imparted to a point on the unsupported edge.

9. In a piezo-electric device of the class described, a support, a slab of Rochelle salt having the' faces substantially parallel to i each other and to the major crystalline'axes and having an edge extending substantially at right angles to the longitudinal axis of the crystal, said edge being securely mounted posed unsupported edge of the slab will have a movement substantially parallel to the sup ported edge upon the applica-tion of an electrostatic field or vice versa.

10. In a piezo-electric device, in combina tion, a support, a slab of piezo-electric ma terial having faces substantially parallel to each other and per endicular to the electric axis of the piezo-e1lectric material, said slab the slab in the direction of ex being secured along one of its edges 'to said support, the free edge portion of said slab, when so arranged, havmg the property of moving parallel to the base a greater linear distance than the movement of the slab in the -to said support whereby a point on the opdirection of expansion or contraction, and a device secured to the free edge of the slab'for utilizing such magnied motion of the slab or imparting motion to the slab.

In testimon whereof I aiix my signature.

HARLES B. SAWYER. 

